Re: 91 5.0 crown vic build?
You cannot legally, anywhere in North America, simply "get rid" of the emission system. By law, those components not only have to exist under the hood, but they must also work. Your vehicle must conform to emission rules, laws & regulations for the year in which it was built. Since your vehicle is a 1991, it is expected that it meets the regulations for 1991.
There is nothing stopping you from simply being rid of it all, but if the car ever needs to pass an emissions test, needs to be certified, or is inspected by a cop with nothing better to do, you can expect some headaches.